I guess it depends on what you define as being a contender. We've seen teams get in that 7th or 8th playoff spot before and make a good run. I would argue that any team in the playoffs is a legitimate contender because you never know what can happen in a 7 game series.
Based on that, I think the Flames a contender before they get a new stadium. Even if a stadium is announced tomorrow you have to imagine it's at least 3 years until you see hockey being played in it.
tl;dr I see the Flames making the playoffs before they set foot in a new stadium.
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